This disclosure concerns an invention relating generally to centrifuges.
A current design of centrifuge has a stationary sun gear about which bobbins rotate in a similar manner to that of the planets around the sun. The bobbins are placed in a framework called the rotor, which ensures that the bobbins can rotate about the sun gear. Attached to each bobbin is a gear which meshes with the sun gear. The flying leads are used to transfer chromatography fluids from the stationary surroundings to the rotating bobbins, where a chromatography process occurs, and then back to the stationary surroundings for processing or analysis.
The weight of the bobbins is taken by bobbin bearings placed between the bobbins and the rotor. The bobbin bearings have to rotate freely while operating under very heavy loads. The current type of bearing used is a rolling element bearing. This type of bearing has rolling elements (e.g., spheres, cylinders, rollers) which rotate between the races. These rolling elements are separated by an item called a cage.
A fundamental problem with this design of centrifuge is that the rolling elements and the cages of the bobbin bearings exert large loads upon each other due to tangential acceleration caused by the motion of the bobbins about the sun gear. These loads greatly increase the frictional torque of the bearing above that normally expected, the theoretical frictional torque. FIG. 1 compares the theoretical and measured torque values for a current design of J-type planet centrifuge. There is a need to increase the performance of these centrifuges which is achieved by increasing the centripetal acceleration generated. The centripetal acceleration can be increased by either increasing the rotational speed or increasing the planetary radius or a combination thereof. As the centripetal acceleration increases so does the tangential acceleration (the tangential acceleration being a component of the centripetal acceleration) acting between the rolling elements and the cages of the bobbin bearings. This in turn increases the frictional torque generated in the bobbin bearings. Higher performance from these centrifuges can be simply achieved by fitting much more powerful drive motors, however this eventually leads to overheating of the bobbin bearings and their failure. The amount of cooling of the bobbin bearings could be increased; however, this adds complexity and weight, the latter aggravating the problem. Increasing the amount of cooling only increases the level of centrifuge performance until the frictional problem of bobbin bearings is reasserted.
The invention involves a centrifuge which is intended to at least partially solve the aforementioned problems. To give the reader a basic understanding of some of the advantageous features of the invention, following is a brief summary of preferred versions of the centrifuge. As this is merely a summary, it should be understood that more details regarding the preferred versions may be found in the Detailed Description set forth elsewhere in this document. The claims set forth at the end of this document then define the various versions of the invention in which exclusive rights are secured.
In a particularly preferred version of the invention, a centrifuge includes a central guide shaft; a plurality of bobbins located around the guide shaft and rotatable therearound; and a support member around the bobbins which provides a substantially cylindrical inner surface around which the bobbins can rotate, and which supports the bobbins. The support member provides means to support the bobbins during rotation thereof and can substantially avoid the aforementioned problems of prior art centrifuges. The support member is preferably free to rotate. This allows for manufacturing variations in the diameter of the bobbins and the diameter of the inner surface of the support member. However, it is possible for there to be a fixed drive ratio between bobbins and the support member if all of these parts are manufactured very accurately.
In one embodiment, the central guide shaft is a rotor, which may be driven to drive the bobbins. In another embodiment, the support member is driven, imparting rotation to the bobbins. Where the guide shaft is a rotor the support member may be fixed; where the support member is rotatable, the guide shaft may be fixed.
There are preferably provided two bobbins, although embodiments have been tested with up to ten bobbins (this not necessarily being the maximum number).
The bobbins advantageously have diameters which are substantially identical, preferably within a tolerance of xc2x10.1%, most preferably of xc2x10.05%. With the preferred embodiment, the actual diameter of the bobbins is not important, solely their relative diameters.
Advantageously, the bobbins are located by plane bearings. This feature assists in location and guidance of the bobbins. These bearings do not support the weight of the bobbins, and rather the support member is supporting this weight. This arrangement avoids the high frictional torque. Alternatives are a needle roller bearing, a hydrostatic bearing in place of a plane bearing, or any other suitable bearing. Similarly, the support member, when rotatable, can be provided with one or more bearings for location and guidance.
The bobbins rotate in the rotor, preferably with no gearing between the rotor and the bobbins. The sun gear, being fixed in space and therefore stationary, meshes with the gears attached the bobbins. The rotor and sun gear have the same central axis. The rotor rotates and the bobbins rotate about the rotor central axis and also about their axis due to the meshing of the sun and bobbin gears.
It is possible with the foregoing preferred versions of the invention to provide speeds of rotation of 1,600 to 3,000 rpm and higher, using motors which would only produce 800 rpm speeds with prior centrifuge designs known to the inventor.
Further advantages, features, and objects of the invention will be apparent from the following detailed description of the invention in conjunction with the associated drawings.